Power amplifier module

ABSTRACT

The present invention provides a power amplifier module featuring that: its output power characteristic smoothly changes as the input control voltage changes; and its control sensitivity is stable over a wide dynamic range. By same means, idling current for gain setting is supplied to a single amplifier element or all of multiple stages of amplifier elements of the power amplifier module. By making this idling current behave so as to exponentially change, relative to input control voltage, the invention enables output power control proportional to the input control voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/878,308filed Jun. 29, 2004 (now U.S. Pat. No. 6,958,656 issued Oct. 25, 2005),which is a continuation of application Ser. No. 09/692,182 filed Oct.20, 2000 (now U.S. Pat. No. 6,771,128 issued Aug. 3, 2004).

FIELD OF THE INVENTION

The present invention relates to a power amplifier module, particularlyto a technology that is effectively applied to a power amplifier modulefor a cellular phone system with the capability of output power controlto be used on portable terminal equipment used in a mobile communicationsystem.

BACKGROUND OF THE INVENTION

Significant growth has lately been found in the market of cellular phonesystems, typically, such as a Global System for Mobile Communication(GSM) and a Personal Communication Network (PCN) and this tendency isanticipated to continue in the future. One of the requirements of suchsystems as GSM and PCN is that the output power of portable terminalequipment can be controlled, dependent on the distance from a basestation to the equipment. This can be fulfilled by controlling the gainof the power amplifier module installed on the equipment.

FIG. 9 shows an example of a typical conventionally used power amplifiermodule with three stages of output power control. In this poweramplifier module, a signal input through a pin 062 is amplified byfirst-stage, second-stage, third-stage amplifiers 601, 602, 603, andoutput through a pin 064. Power source voltage is applied to a pin 063.At this time, an output power control circuit 607 controls the gains ofthe amplifiers 601, 602, and 603 by changing an idling current thatdetermines a DC bias of transistors 604, 605, and 606. Hetero-BipolarTransistors (GaAsHBTs) are used as the transistors 604, 605, and 606.

Using the above third-stage amplifier 603 and its output power controlcircuit 607, the output power control function will be explained below.The amplifier 603 comprises a transistor 606, a resistor 611, couplingcapacitance 612, and an output adjustment circuit 613. The output powercontrol circuit 607 comprises transistors 608, 609, and 610 andresistors 614, 615, and 616. Here, the diode-connected transistors 609and 610 and the diode-connected transistors 608 and 606 form a currentmirror circuit. Current that is as large as mirror ratio times thecurrent flowing across the transistors 609 and 610 flows through thetransistor 606 as the idling current.

The voltage across the transistors 609 and 610 becomes substantiallyconstant when an output power control voltage applied to a pin 061becomes higher than the boot voltage of these transistors. In thevoltage region higher than the boot voltage, the idling currentincreases or decreases in proportion to the control voltage. Because thegain depends on this idling current, the gain can be made variable bycontrolling the idling current. In fact, the output power control usesthis characteristic. In the conventional module example shown in FIG. 9,the idling current to flow in the first-stage amplifier 601 is generatedby applying a voltage produced by dividing the control voltage byresistance to the base of the amplifier. This means taken is differentfrom the means of idling current supply for the second-stage amplifier602 and the third-stage amplifier 603.

SUMMARY OF THE INVENTION

Output power control characteristic requirements are that output powershall change as a monotone function relative to the control voltage in awide dynamic range of 70 to 80 dB (the output power typically rangesbetween −40 and 35 dBm for GSM) and that its change factor, or in otherwords, control sensitivity shall fall within a predetermined value(which is, typically, 150 dB/V or below). In the conventional moduleexample shown in FIG. 9, however, the idling current changes inproportion to the control voltage.

For the circuit shown in FIG. 9, control sensitivity ∂ P₂₁/∂ Vapcbecomes greater as the signal level decreases. This is expressed as:P ₂₁=a constant+20 log I _(d) (dB), I _(d)=(Vapc−2 Vb)/Rapc  (1)∂ P ₂₁ /∂ Vapc=20/(Vapc−2 Vb)(dB/V)  (2)where Vapc>2 Vb∂ P ₂₁ /∂ Vapc=0 where Vapc≦2 Vb  (3)

The above equations (1) and (2), where P₂₁ is gain, I_(d) is idlingcurrent, Vapc is control voltage, Vb is base-emitter voltage of thetransistors 609 and 610, and Rapc is the resistance of the resistor 614,indicate the following. When the control voltage exceeds the sum of theboot voltages of the transistors 609 and 610, the idling current startsto flow, resulting in the greatest control sensitivity. The controlsensitivity becomes theoretically infinity, but there are many caseswhere the input signal power level is actually 0 dBm or higher and theDC current generated by a self-bias effect causes the controlsensitivity to be around 300 dB/V. For equation (3), idling currentI_(d) is generated if Vapc≦2 Vb, but there is no input of the requiredcontrol voltage Vapc, causing that a ∂ P₂₁/∂ Vapc=0.

For the above conventional module example, the first-stage amplifier601, the second-stage amplifier 602, and the third-stage amplifier 603operate in different states. Due to this, a kink is liable to take placein the control characteristic, which made it difficult to satisfy theoutput power control characteristic requirements of the power amplifiermodule. As apparent from a characteristic chart shown in FIG. 10, thecontrol characteristic greatly changes, depending on the power at theinput signal pin, and a control voltage Vapc level section representingextremely high sensitivity appears. When the sensitivity becomesextremely high as the characteristic chart shows, the output power Poutgreatly changes with even small change of the control voltage Vapc. Whena feedback to return such excessive change of the output power Pout tonormal is applied, the characteristic also responds to the feedback andsuch a oscillation state appears that the output power Pout cyclicallychanges for a period corresponding to the feedback loop.

An object of the present invention is to provide a power amplifiermodule featuring that its output power characteristic smoothly changesas the input control voltage changes and that its control sensitivity isstable over a wide dynamic range. Another object of the presentinvention is to provide a power amplifier module of convenient service.The above and other objects as well as noticeable features of thepresent invention would be elucidated from the whole text of the presentspecification and the related drawings.

A typical power amplifier module embodied by the invention disclosedherein will be summarized below. The power amplifier module accomplishesoutput power control in such a manner that: upon the reception ofcontrol input voltage, idling current is generated and adjusted suchthat it exponentially changes, relative to the control input voltage andthe idling current is supplied to a power amplifier element.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparentduring the following discussion of the accompanying drawings, wherein:

FIG. 1 is a basic circuit diagram showing a power amplifier module as apreferred embodiment of the present invention;

FIG. 2 is a circuit diagram showing a power amplifier module as anotherpreferred embodiment of the present invention;

FIG. 3 is a circuit diagram showing a concrete power amplifier module asanother preferred embodiment of the present invention;

FIG. 4 is a circuit diagram showing another concrete power amplifiermodule as another preferred embodiment of the present invention;

FIG. 5 is a block diagram showing a power amplifier module ofthree-stage configuration as another preferred embodiment of the presentinvention;

FIG. 6 is a block diagram of a power amplifier module as anotherpreferred embodiment of the present invention;

FIG. 7 is a characteristic chart for explaining the operation of poweramplifier modules that are embodiments of the present invention;

FIG. 8 is an overall block diagram of mobile communication equipment asa preferred embodiment on which a power amplifier module offered by thepresent invention is used;

FIG. 9 is a circuit diagram showing an example of prior art; and

FIG. 10 is a characteristic chart for explaining the operation of thepower amplifier module shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a basic circuit diagram of a power amplifier module as apreferred embodiment of the present invention. Any of the circuitelements in FIG. 1 is a discrete circuit module comprising a singlesemiconductor integrated circuit or a plurality of semiconductorintegrated circuits and an external component connected to it or them.The power amplifier module of first embodiment comprises an amplifier 6that consists of an output transistor 2, an adjustment circuit 4, andcoupling capacitance 5 and an output power control circuit 1 thatconsists of a V-I logarithmic conversion circuit 11, a constant currentsource 7, input transistors 3 and 8, and an impedance circuit 9.

The V-I logarithmic conversion circuit 11 executes logarithmicconversion of an input control voltage, that is input through a pin 03,into current. This circuit 11 enables the idling current in the outputtransistor 2 to exponentially change relative to the input controlvoltage. The transistor 8 supplies the DC component of a base currentthat is generated, as an increment by the self-bias effect during thelarge-signal operation mode, and flows across the output transistor 2.

The impedance circuit 9 is used to prevent the instability of operationdue to that a high-frequency signal of the input signals input throughthe pin 01 flows through the above-mentioned input transistor 3.Reference number 04 is a power source pin. The input transistor 3 formsa current mirror circuit in conjunction with the output transistor 2 andhas a current sensing function. Therefore, when a reference current fromthe constant current source 7 is allowed to flow across the inputtransistor 3, current that is as large as mirror ratio times thereference current is allowed to flow across the transistor 3 as theidling current.

In the above-mentioned conventional module example shown in FIG. 9, theidling current changes in proportion to the control voltage, whereas, asa feature of the circuitry of this first embodiment, the idling currentis adjusted such that it exponentially changes, relative to the inputcontrol voltage. The following equations give gain P₂₁ and controlsensitivity ∂ P₂₁/∂ Vapc in small-signal operation mode of firstembodiment:P ₂₁=a constant+α Vapc/Vt×20 log e (dB),I _(d) =I _(s) exp(α Vapc)  (4)∂ P ₂₁ /∂ Vapc=α/Vt×20 log e=347α (dB/V)  (5)

where I_(s) and Vt (up to 25 mV) are physical constants and α is acoefficient. Equation (4) indicates that the gain is proportional to theinput control voltage Vapc. From this, as is indicated in equation (5),it is seen that control sensitivity is constant in the present inventionand desired control sensitivity can be obtained if coefficient α is setat a suitable value. For example, set coefficient α at 0.5 or less inorder to give control sensitivity of 150 dB/V or below. This isattributed to the adjusted behavior of the idling current I_(d) thatexponentially changes, relative to the input control voltage Vapc. Mostpower amplifier modules used for practical application consist of aplurality of amplifiers. In practical situations, it is advisable tosuitably allot the desired control sensitivity required for a poweramplifier module among the multiple stages of amplifiers, according totheir capabilities.

In the present invention, the relation of exponential function betweenthe current supplied from the constant current source 7 and the inputcontrol voltage Vapc holds true. Thus, the idling current I_(d)exponentially changes, relative to the input control voltage Vapc, aswas indicated in equation (4). Here, the value of the idling currentI_(d) is determined from such DC bias of the output transistor 2 as togive desired output power and efficiency. On the other hand, an inputsignal is input through a pin 01, passes through the couplingcapacitance 5, and after being amplified through the output transistor 2and the adjustment circuit 4, it is output through a pin 02. Because theidling current I_(d) exponentially changes, relative to the inputcontrol voltage Vapc, the gain (dB), or in other words, output power(dBm) increases or decreases in proportion to the input control voltageVapc.

Therefore, constant control sensitivity such as a value of 347α (dB/V)for an input control voltage Vapc, as was indicated in equation (5), canbe obtained. During the operation explained above, a smooth output powercontrol characteristic with little kinks can be measured as apparentfrom the characteristic chart shown in FIG. 7. Here, even if the powerat the input signal pin is variable among decibel values −4 dBm, 0 dBm,4 dBm, and 6 dBm, stable output power control can be achieved. In thisway, the invention can provide a power amplifier module with anexceedingly good control characteristic and of convenient service.

For the transistors 2, 3, and 8, any type of bipolar transistors such asGaAsHBTs, SiGeHBTs, or Si bipolar transistors can be applicable, as willbe described later. Because the transistors 2 and 3 form a currentmirror circuit, it is desirable that they are same type transistors andintegrated on a same chip. For a current supply circuit 10 that suppliescurrent to the transistors 2 and 3, an integrated circuit to which Sibipolar process is applied as well as HBT may be used. The V-Ilogarithmic conversion circuit 11 and the constant current source 7 maybe any circuit type, provided they function, assuring that the referencecurrent flows across the transistor 3, while changing exponentially,relative to the control voltage.

FIG. 2 shows a circuit diagram of a power amplifier module as anotherpreferred embodiment of the present invention. This second embodimentmodule comprises three stages of power amplifiers connected in tandem.This configuration of the power amplifier module may comprise two stagesfor systems of relatively small output power requirement, for example,such as a Code Division Multiple Access (CDMA) system.

Unlike the above-mentioned conventional multi-stage amplifier moduleshown in FIG. 9, three stages of amplifiers of second embodiment aresupplied with the reference current that determines the idling currentto flow through the transistors in the stages from an output powercontrol circuit 101 that executes control operation by same means. Theidling currents flowing across transistors 105, 106, and 107 foramplification (corresponding to the above-mentioned transistor 2) inamplifiers 102, 103, and 104 are as large as mirror ratio times thecurrents flowing across current sensing transistors 108, 109, and 110(corresponding to the above-mentioned input transistor 3), respectively.

Note that different current mirror ratios are set for the amplifiers102, 103, and 104, according to the difference in the dimensions of thetransistors 105 and 108, the transistors 106 and 109, and thetransistors 107 and 110. The smallest mirror ratio is set for thefirst-stage transistor 105 for which the smallest operating power isrequired. The greatest mirror ratio is set for the last-stage transistor107 for which the greatest operating power is required. The greater themirror ratio, the greater the idling current flows through thetransistor.

According to the second embodiment, the transistors 105, 106, and 107carry different idling currents that are determined by different currentmirror ratios as described above, and consequently the amplifiersfundamentally operate in the same manner even if input power levels aredifferent. Therefore, the amplifier module can be embodied, exhibitingthe smoother output power control characteristic apparent from thecharacteristic chart shown in FIG. 7, as compared with the conventionalmodule example where the first-stage amplifier and the second-stage andthird-stage amplifiers operate in different manners. In fact, the outputpower characteristic of the combined amplifiers of second embodimentexhibits smooth linear change with little kinks, which is made possibleby the present invention.

Then, the circuit operation of second embodiment will be explainedbelow. An input signal is applied to a pin 011 of the power amplifiermodule. The input signal passes through an adjustment circuit 111 wherethe signal source impedance is adjusted to an impedance match for inputto the transistor 105 and is conveyed to the transistor 105 where itspower is amplified. The amplified signal passes through an adjustmentcircuit 112 where the output impedance of the transistor 105 is adjustedto an impedance match for input to the transistor 106 and is supplied tothe base of the transistor 106.

The signal thus conveyed to the transistor 106 is similarly conveyedfrom the transistor 106 through an adjustment circuit 113 to thetransistor 197 and passes through an adjustment circuit 114, duringwhich its power is serially amplified, and eventually it is outputthrough a pin 012. As described above, a constant value of controlsensitivity is given for a control voltage. If the amplifiers 102, 103,and 104 respectively have control sensitivity ∂ P₂₁/∂ Vapc, controlsensitivity ∂ P′₂₁/∂ Vapc, and control sensitivity ∂ P″₂₁/∂ Vapc, thecontrol sensitivity of the whole power amplifier module ∂ P₀₂₁/∂ Vapc isgiven by:∂ P ₀₂₁ /∂ Vapc=∂ P ₂₁ /∂ Vapc+∂ P′ ₂₁ /∂ Vapc+∂ P″ ₂₁ /∂ Vapc  (6)The result is the sum of the values of control sensitivity of allamplifiers stages.

Equation (6) indicates that desired control sensitivity of the module isobtained by assigning required sensitivity components to the stages ofamplifiers and the percentages of the components are optional. Ifdesired control sensitivity is, for example, 150 dB/V or below and itseven components are assigned to the amplifier stages, assign controlsensitivity of 50 dB/V or below to each stage of amplifier so that theintention can be met.

A current supply circuit 115 or the amplifiers and the output powercontrol circuit may be integrated on a single chip by applying Sibipolar transistors and SiGeHBT process. It is desirable to integratethe transistors 105 through 110 on a same chip in order to reduce thesize of the power amplifier module as well as provide uniformcharacteristics.

FIG. 3 shows a circuit diagram of a concrete power amplifier module asanother preferred embodiment of the present invention. An output powercontrol circuit 350 is to establish the relation of exponential functionbetween the idling current and the control voltage such that the idlingcurrent exponentially changes, relative to the control voltage. For thispurpose, it is advisable to make the reference current behave as theexponential function of the control voltage when flowing across an inputtransistor 316 that forms a current mirror circuit in conjunction withan output transistor 317.

The method and circuit operation for embodying this will be describedbelow. First, a V-I conversion circuit 351 generates current that isproportional to the input control voltage Vapc that is input through apin 013. When the input control voltage Vapc exceeds the base-emittervoltage of a transistor 302, the current determined by a resistor 301starts to flow through the transistor 302. Because the transistors 302and a transistor 303 form a current mirror circuit, current that is aslarge as mirror ratio times the current flowing through the transistor302 then starts to flow across the transistor 303.

After a current mirror circuit formed by transistors 304 and 308reverses-the direction of the current, the current is supplied via atransistor 309 to a resistor 307 and converted into voltage again. Atthis time, a transistor 305 supplies current to a transistor 306,thereby forming a pseudo voltage source. Voltage to be generated in theresistor 307 changes from the origin voltage that is generated by theabove pseudo voltage source, that is, the base-emitter voltage of thetransistor 306. The above process is carried out as preparation forestablishing the relation of exponential function between the referencecurrent to flow across a transistor 316 and the input control voltageVapc. Meanwhile, because the voltage occurring across the resistor 307is proportional to the input control voltage Vapc, a value of the αcoefficient in the equations (4) and (5) can be determined by using theratio of the resistance of the resistor 307 to the resistance of theresistor 301, which eventually can determine control sensitivity.

For example, increasing the resistance of the resistor 307 causescontrol sensitivity to increase because the voltage across the resistor307 rises; inversely, decreasing the resistance causes controlsensitivity to decrease. This means that control sensitivity can bedetermined by properly selecting a value of the α coefficient. The αcoefficient primarily depends on the relative ratio of the resistance ofthe resistor 307 to the resistance of the resistor 301. Thus, the valueof α is substantially constant, regardless of the productive deviationof the resistors. In other words, the control circuit of thirdembodiment has control sensitivity that is not susceptible to productivedeviation, provided its circuit elements are packaged on a singlesemiconductor integrated circuit.

The voltage occurred across the resistor 307 is conducted vialevel-shift transistors 309 and 311 to the base of a transistor 312where it is converted into a collector current of the transistor 312. Atthis time, because the emitter of the transistor 312 is grounded, thecollector current is caused to exponentially change, according to therelation of exponential function between the current and the basevoltage, that is, input control voltage Vapc.

After its direction is reversed by a current mirror circuit formed bytransistors 313 and 314, that is, a constant current source, thiscollector current is supplied to the transistor 316 as referencecurrent. A temperature characteristic control circuit 353 performs thetask of adjusting the temperature characteristic of the referencecurrent flowing through the transistor 316. Because the base-emittervoltage of the transistor 317 has a negative coefficient of temperature,the collector current continues to increase as temperature rises. Thetemperature characteristic control circuit 353 sets the temperaturecharacteristic of the reference current to be supplied to the transistor316 so that the coefficient of temperature of the current at hightemperature will be less than the coefficient of temperature of thecurrent at normal temperature. In this way, the circuit 353 functions tosuppress the increase of the current due to the rise of the temperatureof the transistor 317.

A transistor 315 supplies the DC component increment of the current toflow in the base of the transistor 317 when an amplifier 356 operates inlarge-signal mode. The output power control circuit 350 can beintegrated by the Si process. However, the transistor 316 and thetransistor 317 are same devices and should be integrated on a same chip.

FIG. 4 shows a circuit diagram of another concrete power amplifiermodule as another preferred embodiment of the present invention. Thiscircuit of fourth embodiment has an additional output limit function. Tothe collector of a transistor 312 where the idling current is generatedthat exponentially changes as described above, a resistor 318 isconnected. Voltage occurring across the resistor 318 is applied to thebase-emitter of a transistor 319. The transistor 319 performs outputlimit action by using its base-emitter voltage as a reference voltagefor limiting. Specifically, when the voltage drop occurring as theoutput current from the transistor 312 flows across the above resistor318 exceeds the base-emitter voltage of the above transistor 319, thetransistor 319 is activated and forms a bypass path of the current froma power source pin 04 to the collector of the transistor 312.Consequently, even if the above input control voltage Vapc furtherincreases, which in turn increases the control current generated in thetransistor 312, the increment of the current flows through thetransistor 319. Therefore, the current to be supplied to the abovetransistor 313 is constant and the gain of the output transistor 317 islimited.

FIG. 5 shows a block diagram of a power amplifier module of three-stageconfiguration as another preferred embodiment of the present invention.An output power control circuit 501 that controls the idling currentsupply to an amplifier 510 may be configured such that the controlcircuit 350 in FIG. 3 or FIG. 4 and its duplicates, a total of threecontrol circuits are used in tandem as presented in FIG. 2. In thisfifth embodiment, however, for circuit simplification purposes, thecircuit 501 is configured as follows. A V-I current conversion circuit351, a circuit for setting of coefficient of I-V conversion 352, atemperature characteristic control circuit 353, and a V-I logarithmicconversion circuit 354 are common ones that are shared with three stagesof amplification. Only a current supply circuit 355 is configured tohave three stages for three stages of amplification in the amplifier510, comprising three constant current sources, each of which consistsof the transistors 313 and 314 in FIG. 3 or FIG. 4 and three DCsupplies, each of which consists of the transistors 315 and 316 thatsupply DC current and idling current to the transistor 317. The basicoperation of the fifth embodiment module is the same as that of theembodiment shown in FIG. 2 and its explanation will not be repeated.

FIG. 6 shows a block diagram of a power amplifier module as anotherpreferred embodiment of the present invention. In this sixth embodimentmodule, there are two duplicated systems of the output power controlcircuits 501 shown in FIG. 5 to operate for two different systems, forexample, GSM and PCN systems. These output power control circuits 591have a function of switching between amplifiers 511 and 512. The moduleincludes circuits 502 and 504 for switching between both amplifiers by aVcnt control signal that is input through a pin 052 and current limitcircuits 503 and 505 for limiting a rapidly increasing reference currentdue to the rise of control voltage as described above with FIG. 4.

Switching between the amplifiers is performed in accordance with, forexample, the following condition setting. When the Vcnt control signalis “High” level (lower than 2 V), the amplifier for GSM system is activeand the other amplifier for PCN system is inactive. When the Vcntcontrol signal is “Low” level, inversely, the amplifier for GSM isinactive and the other amplifier for PCN is active. Alternatively, theabove levels of the Vcnt control signal may be upside down.

The current limit circuits 503 and 505 in FIG. 6 can be embodied asfollows. As shown in FIG. 4, the resistor 318 for current sensing isconnected to the collector end of the transistor 312 and both ends ofthe resistor 318 are connected to the base-and-emitter-coupledtransistor 319 for current bypassing. Because the voltage across theresistor 318 becomes substantially constant when it exceeds thebase-emitter voltage of the bypassing transistor 319, further extracurrent is bypassed via the transistor 319. In this way, theabove-mentioned current limit function can be implemented. The currentlimit level is determined by the resistor 318.

FIG. 8 shows an overall block diagram of mobile communication equipmentas a preferred embodiment on which a power amplifier module offered bythe present invention is used. A typical example of this mobilecommunication equipment is a portable mobile phone as mentioned above.Signals received by an antenna are amplified in a receive front-end,converted into an intermediate frequency by a mixer, and conveyedthrough an intermediate signal processing circuit IF-IC to a toneprocessing circuit. A gain control signal periodically included amongthe above received signals is decoded in a microprocessor CPU, which isnot limited to a specific one, where an input control voltage to besupplied to a power amplifier (power amplifier module) is generated.

The power amplifier executes gain control in accordance with the aboveinput control voltage and generates a send output signal. Part of thepower loss is fed back to the above microprocessor CPU via a powercoupler so that power control within a given range is performed asexplained above. A frequency synthesizer generates an oscillating signalcorresponding to the received signal frequency by using a referenceoscillator TCXO, a voltage control oscillator VCO, and a PLL loop. Thisoscillating signal is conveyed to the mixer in the receive front end andsupplied to a modulator as well. In the above tone processing circuit,the received signal drives a receiver from which a tone signal isoutput. Voice to send is converted into electric signals in a microphoneand the signals are conveyed through the tone processing circuit and amodulator/demodulator to the modulator.

In such mobile communication equipment, the above power coupler is usedor the power source current flowing in the power amplifier circuit issensed to determine whether power output operation is performed within agiven range as specified for send operation and a feedback signal isgenerated. By means of such feedback loop, the power amplifier executesgain control operation and this may cause oscillation. This oscillationmechanism is as follows. If a partial range of control sensitivity toinput control voltage is extremely high, the output power excessivelychanges when the corresponding input control voltage is supplied.Feedback action to return the excessive change to normal recurs at delaytiming during a feedback loop and this causes the output power tofluctuate largely.

Because a maximum distance between base stations is 10 miles (about 16km), permitted for the above-mentioned GSM system, the output of aportable mobile phone must be controlled on a level ranging between 13dBm and 43 dBm in 2-dB steps. This output control always controls thesend power output of the portable mobile phone. In fact, the outputcontrol operation must be performed in accordance with control signalsperiodically transmitted from a base station. The power amplifier moduleprovided by the present invention has substantially constant controlsensitivity for all the region of input control voltages. Its stablecontrol sensitivity over a wide dynamic range enables mobilecommunication equipment such as the above portable mobile phone toexecute high-quality signal transmission.

According to the present invention, as explained above, the idlingcurrent to flow the power amplifier module exponentially changes,relative to output power control signals. Thus, the invention enablesproportional or linear gain (dB) control in accordance with the inputcontrol voltage, providing required stable control sensitivity. Asconcerns a power amplifier module of multistage configuration, forexample, two stages or three stages, because idling current supply toeach amplifier stage for power control is performed by same means, themodule can be designed to exhibit a good control characteristic withlittle kinks. Furthermore, the invention is beneficial for costreduction because the output power control circuit can be fabricatedwith Si bipolar transistors and the power amplification stages may befabricated with GaAsHBT, SiGe-HBT, and Si bipolar transistors incombination.

The forgoing embodiments produce the following effects:

-   (1) A power amplifier module accomplishes output power control in    the following way: upon the reception of control input voltage,    idling current is generated and adjusted such that it exponentially    changes, relative to the control input voltage and the idling    current is supplied to a power amplifier element. As the input    control voltage changes, the output power characteristic smoothly    changes. The power amplifier module features stable control    sensitivity over a wide dynamic range.-   (2) In addition, a control circuit for implementing the above    control is configured with a circuit for converting the input    control voltage into current, a circuit for generating a reference    voltage from the current into which the input control voltage has    been converted and setting a gradient of voltage that changes in    proportion to the input control voltage, and a circuit for    converting the voltage into the idling current that exponentially    changes. Thereby, required stable control sensitivity can be set.-   (3) In addition, the power amplifier module is configured with a    plurality of stages of amplifiers connected in tandem and a    plurality of control circuits that receive the control input voltage    in common and separately supply the idling current to one of the    stages of amplifiers. Because the amplifier stages operate-in the    same way, the power amplifier module can be designed to exhibit a    good control characteristic with little kinks.-   (4) In addition, the power amplifier module uses a common control    circuit comprising the circuit for converting the input control    voltage into current, the circuit for generating a reference voltage    from the current into which the input control voltage has been    converted and setting a gradient of voltage that changes in    proportion to the input control voltage, and the circuit for    converting the voltage into the idling current that exponentially    changes. This eliminates the possibility of supply of varying idling    currents which otherwise might occur among a plurality of idling    current generators. The power amplifier module further includes a    plurality of circuits for supplying the idling current to the    multiple stages of amplifiers such that each circuit serves each    amplifier with the idling current. In this way, the entire module    circuit can be designed to be simple.-   (5) In addition, the amplifier is fabricated with GaAsHBTs packaged    on a semiconductor integrated circuit including a pair of an input    transistor and an output transistor; the input transistor carries    the above idling current and forms a current mirror circuit in    conjunction with the output transistor. The control circuit is    fabricated with Si transistors or GaAsHBTs packaged on a    semiconductor integrated circuit. Thereby, high-frequency power    output operation required for portable mobile phones can be    implemented.-   (6) In addition, the amplifier is fabricated with SiGeHBTs or Si    bipolar transistors packaged on a semiconductor integrated circuit    including a pair of an input transistor and an output transistor;    the input transistor carries the idling current and forms a current    mirror circuit in conjunction with the output transistor. The    control circuit is fabricated with SiGeHBTs or Si bipolar    transistors. Thereby, high-frequency power output operation required    for portable mobile phones can be implemented.-   (7) In addition, the power amplifier module further includes a    circuit for limiting the idling current when the input control    voltage has reached a certain level. Thereby, the module can be    designed to perform stable operation with low power consumption.-   (8) In addition, the power amplifier further includes a circuit by    which the temperature characteristic of the idling current can be    set optionally. Thereby, stable power output operation not    susceptible to ambient temperature can be achieved.

The present embodiments explained above are to be consideredillustrative and the present invention is not limited to the foregoingembodiments. Of course, the invention maybe embodied in othermodification forms within a-scope not departing from the spirit oressence thereof. For example, for the first embodiment shown in FIG. 1,the input transistor 3 that is used as a reference current sensingdevice is not limited to some transistor type. Instead, a diode ordiode-connected transistors of the same material as the transistor 2 foramplification may be used. This substitution does not alter the relationof exponential function between the input control voltage and the idlingcurrent.

Mobile communication equipment to which the present invention is appliedincludes, in addition to those such as mobile phones that perform toneor voice signal transmission/reception, those that perform digitalsignal transmission/reception to/from a personal computer or othersimilar mobile communication equipment via a digital telephone switchnetwork by converting digital signals into signals in a tone signalfrequency band. For such digital signal transmission/reception, thepresent invention makes the transmission signal level stable, which canachieve data communications at a higher rate. The present invention canbe widely used for power amplifier modules used on such mobilecommunication equipment.

A typical implementation of the invention disclosed herein produceseffects that will be summarized below. According to the presentinvention, idling current to flow a power amplifier exponentiallychanges, relative to output power control signals, so that gain can becontrolled in proportion to the control voltage and required controlsensitivity can be obtained. For a power amplifier module of two-stageor three-stage configuration, because idling current supply to eachamplifier stage for power control can be performed by same means, themodule can be designed to exhibit a good control characteristic withlittle kinks.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been changed in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

1. A power amplifier module comprising: an amplifier including an outputtransistor; and a control circuit for supplying the amplifier with anidling current that controls the output power of the amplifier, whereinthe control circuit includes: an input transistor carrying the idlingcurrent and forming a current mirror circuit in conjunction with theoutput transistor, and an impedance circuit coupling a base of the inputtransistor with a base of the output transistor, and wherein the controlcircuit receives input control voltage and makes the idling currentbehave so as to exponentially change relative to the input controlvoltage.
 2. The power amplifier module according to claim 1, wherein thecontrol circuit includes: a circuit that converts the input controlvoltage into current; a circuit that generates a reference voltage fromthe current into which the input control voltage has been converted andsetting a gradient of voltage that changes in proportion to the inputcontrol voltage; and a circuit that converts the voltage into the idlingcurrent that changes exponentially relative to the input controlvoltage.
 3. The power amplifier module according to claim 1, wherein theamplifier is a complex comprising a plurality of stages of amplifiersconnected in tandem, and wherein the control circuit is a complexcomprising a plurality of circuits that receive the control inputvoltage in common and separately supply respective idling currentsbehaving as aforesaid to the plurality of stages of amplifiers.
 4. Thepower amplifier module according to claim 3, wherein a common circuit isformed, comprising the circuit that converts the input control voltageinto current, the circuit that generates a reference voltage from thecurrent into which the input control voltage has been converted andsetting a gradient of voltage that changes in proportion to the inputcontrol voltage, and the circuit that converts the voltage into theidling current that changes exponentially, and wherein a plurality ofcircuits connected to said common circuit supply the respective idlingcurrents to the plurality of stages of amplifiers.
 5. The poweramplifier module according to claim 1, wherein the power amplifiermodule further includes a circuit that limits the idling current oncethe input control voltage has reached a predetermined level.
 6. Thepower amplifier module according to claim 1, wherein the power amplifiermodule further includes a circuit by which a temperature characteristicof the idling current can be set optionally.
 7. The power amplifiermodule according to claim 2, wherein the amplifier is a complexcomprising a plurality of stages of amplifiers connected in tandem, andwherein the control circuit is a complex comprising a plurality ofcircuits that receive the control input voltage in common and supplyrespective idling currents behaving as aforesaid to the plurality ofstages of amplifiers.
 8. The power amplifier module according to claim7, wherein a common circuit is formed, comprising the circuit thatconverts the input control voltage into current, the circuit thatgenerates a reference voltage from the current into which the inputcontrol voltage has been converted and setting a gradient of voltagethat changes in proportion to the input control voltage, and the circuitthat converts the voltage into the idling current that changesexponentially relative to the input control voltage, wherein a pluralityof circuits connected to said common circuit supply the idling currentsto the plurality of stages of amplifiers.